Method of reducing ores



F. HODSON ETAL METHOD OF REDUCING ORES Filed Dec. 26, 1939 se ns, 1942.

Eh R FRANK l X0565? iaosou a M ATTORNEY.

Patented Sept. 8, 1942 UNITED STATES PATENT OFFICE METHOD OF REDUCINGORES Application December 26, 1939, Serial No. 310,860

27 Claims.

This invention relates to methods of and means for reducing ores,especially those such as antimony sulfide and the like wherein the metalcontent is capable of being converted into a fume.

At present many diiferent methods are employed to reduce such ores butall are unsatisfactory in that they are incapable of producingsubstantially pure metal at a cost which permits it to be usedcommercially to any great extent.

In accordance with the present invention, however, an ore of this sortand particularly antimony sulfide ore may be reduced to a desired stateat a cost far below the cost at which it could be reduced to a likestate by methods heretofore practiced. Briefly this is accomplished by.

passing the ore to be heated through an oxidizing zone maintained attemperatures suflicient to convert the metal content thereof to a fume,and then passing the fume thus formed without allowing any substantialcondensation or coagulation thereof through a reducing zone maintainedat temperatures suflicient to reduce the fume to the desired state.

The ore is preferably ground to a very fine particle size prior to theoxidizing or roasting operation since this leads to economy in fuel andrapidity of roasting by virtue of the .added surface area and ease ofgas penetration thus provided by the finely divided particles. Inaddition, the powdered ore and air required during the roastingoperation are preferably pre-heated, this being desirable since itspeeds up the roasting reaction and makes possible a considerable savingin fuel.

Also, the reduction of the fume is preferably example, but obviouslymany changes and variations may be made therein and in its mode ofoperation, which will still be confined within the spirit of theinvention, and it is to be understood, therefore, that the invention isnot limited to any specific form of embodiment, except insofar as suchlimitations are specified in the claims.

In describing the invention, the reduction of antimony sulfide ore hasbeen chosen for purposes of illustration, this being done since this oreis typical of the type of are which may be efiected in an atmospherewhich is maintained the blower l1.

reduced with advantage in accordance with the teachings of the presentinvention.

In practicing the invention with the apparatus shown, the ore is firstpulverized and then loaded into a hopper Ill, from whence it is fed intoa horizontally disposed feed screw conveyor ll capable of being drivenat any desired rate of speed by means of a motor or the like (notshown). The conveyor H for the major part of its length is housed in theenlarged horizontal portion of an inverted U-shaped pipe l2, which opensat one end into the upper part of a vertically disposed air chamber I3housed in a preheating furnace I4 and at its other end into the upperend of a vertically disposed roasting chamber I5 housed in a recuperatorfurnace l6.

An air or other oxidizing gas stream created by a blower II, asindicated by the arrows in the drawing, travels upwardly through thevertically disposed air chamber l3, through the inverted U-shaped pipeI2 in which the conveyor II is housed, and thence downwardly through theroasting chamber l5. As the oxidizing gas stream passes upwardly throughthe chamber l3, it is preheated by hot waste gases in the mannerhereinafter explained, and as this preheated gas stream travels throughthe inverted U-shaped pipe II, the pulverized ore in the conveyor II ispreheated by indirect heat transfer as its passes therethrough. Anyvaporized moisture which may form in the conveyor ll during thepreheating of the ore will be carried away by means of a manifold l8incorporated in the upper part of the conveyor H and so positioned thatwhile water vapor is being discharged the heated air in the invertedU-shaped pipe l2 cannot blow back.

The conveyor II preferably discharges the dry powdered ore into theinverted U-shaped pipe I2 beyond the beginning of the bend which leadsdownwardly into the roasting chamber I5, this being desirable so thatthe ore will be delivered into the chamber l5 by gravity, as well asunder the influence of the air or gas stream set up by The amount ofoxidizing gas thus directed through the chamber I5 is such as to ensurethe complete 'oxidization of the ore, it being controlled by a damperI9, and the chamber 15 is maintained at temperatures (350 to 450 C.)sufficient to roast the ore and bring about the conversion of theantimony content to antimony trioxide fume and the sulphurcontent tosulphurous gases; and here it is to be noted that the roasting chamberI5 is of greater cross-section than that of the lower end of theinverted V-shaped pipe l2 which opens into it so that the stream will beslowed down to ensure substantially complete roasting and volatilizationof the ore as it travels therethrough. In this phase of the cycle ofoperations, however,

care must be exercised to insure that the temperature of the chamber I5is not raised sufliciently high (800 C.) to convert the antimony contentof the ore into the stable antimony tetroxide.

From the roasting chamber IS, the stream of antimony trioxide fume, thesulphurous as well as any other gases which might be created during theroasting process, and the solid gangue particles, are directeddownwardly through a pipe l5a, as indicated by the arrows in thedrawing, to a collector 20, which is maintained at temperaturessufficiently high, to prevent the antimony trioxide fume content of thestream from coagulating and condensing therein. As the stream ofantimony trioxide fume, solid gangue particles and gases pass throughthe collector 20, the solid gangue particles settle to the bottom andinto a heat insulated hopper 2|, from whence they may be removed bymeans of a screw conveyor 22.

From the gangue collector 20 the stream which now comprises antimonytrioxide fume and the gases created during the roasting operation isdirected into the lower end of a vertical shaft furnace 24by means of apipe 23 having a dis.-

charge end adapted to direct the incoming stream upwardly through thecentral portion of the furnace 24 towards its dome shaped top. As thestream enters the furnace 24, a mixture of preheated air or otheroxidizing gas and powdered coal or other carbonaceous fuel is injectedtherein and in such a manner that the combined stream of antimonytrioxide fume, the gases created during the roasting operation and theinjected oxidizing gas and fuel is forced upwardly through the furnace24 at high velocity. As the upwardly flowing center stream nears the topof the furnace 24 its direction of travel is reversed and it then flowsdownwardly about the upwardly flowing center stream in the form of atubular envelope. The powdered fuel thus injected into the pipe 23 isstored in a hopper 25 and thepreheated oxidizing gas is conveyed througha pipe 2' to the pipe 23 from the narrow lower end of the invertedU-shaped pipe I2 opening from the air chamber l3 through which thepreheated air stream flows with high velocity, and the arrangement ofparts is such that the air carries the fuel from the hopper 25 into thepipe 23 in syphon fashion. Instead of powdered fuel a reducing gas, suchas water gas, may be used. The pipe 26 carrying the preheated air isprovided with a valve 21 for regulating the amount of air injected intothe pipe 23, and enough fuel must be used with this air to heat thefurnace 24 to approximately 800 C., and to supply carbon or otherreducing medium to reduce this antimony trioxide fume, as well as tokeep the atmosphere within the furnace 24 strongly reducing in nature.

In the furnace 24 the antimony trioxide fume is reduced to metaldroplets, the speed of the reaction being promoted-by the violentturbulence therein which, in keeping the materials in a constantco-mingled and agitated state, prevents envelopes of non-reducing gasesfrom forming about partially reduced molecules of this trioxide fume.

In the hotter portions of the furnace 24 it is possible that someantimony tetroxide may be formed by oxidation of the antimony trioxide,but if it is formed it will also be reduced by the reducing mediumpresent. In addition, any carto carbon monoxide by theaction of the freecarbon present, and so assist instantaneous reduction of the antimonytrioxide fume.

From the furnace 24 the stream of antimony metal droplets and theresultant gases is directed into and through a heat insulated collectingchamber ll. The chamber 30 is of larger cross section than that of thefurnace 24 so that the stream will be slowed down to the point where themetal droplets will fall to the bottom. To further promote theseparation of the metal from the gases, the chamber 30 is provided withan extension 30a having baflles 3| secured to the top and bottom wallsthereof over which the stream must pass, and to permit the metal todrain from the extension 30a back into the chamber 30, the baffles 3|secured to the bottom wall are provided with apertures Sla.

During the separation of the metal in the chamber 30 some carbon matteror ash may also settle out, but since it is much lighter than antimony,it will float on top of the metal and so form a protective coatingthereon. v

The chamber 30 is provided with a door 32 through which the antimonymetal can be worked or ladled out under cover of a starting mixture andpoured intomolds or, if desired, run off into another ,fumace forfurther working or refining, if the quantity or nature of any impuritiespresent makes this necessary.

From the metal collecting chamber, the stream of gases is conductedthrough a pipe 33 to the recuperator furnace 16 which heats the roastingchamber l5, and to maintain the temperature thereof at desired valuesthe unburnt gases in the stream are burnt by admitting a portion of thestream of preheated air or other oxidizing gas created by the blower I!through a pipe 34, the amount of air thus admitted being regulated by avalve 35.

From the recuperator furnace IS the stream of hot gases is conducted toa housing 36 which surrounds the upper part of the gangue collector 20but which is'separated from it by a gas tight heat transmitting wall 31.By this arrangement the gangue collector 20 is kept hot enough byindirect heat transfer to prevent the coagulation and condensation ofthe antimony trioxide fume contained in the mixture of gas and gangueparticles, which are discharged therein from the lower end of theroasting chamber IS.

From the housing 36 the stream of gases flows through a conductor 40into the lower end of the preheating chamber l4 from whence it passesupwardly about the chamber 13 to preheat the actuating stream of aircreated by the blower I].

From the preheater [4 the stream of gases is led off by a stack 42 forthe removal of the sulphur content, as well as for further utilizationof any other valuable gases which might be present.

If an ore containing arsenic is used, the proces of reduction is thesame as outlined above.

A mixtureof arsenic trioxide and antimony tribon dioxide that may beformed will be reduced oxide is formed in the roasting chamber l5 andsince both are volatile at' the temperature of roasting, they both takethe form of fume and after the gangue has been separated out in the'collector 24 they pass through the pipe 23 along above the meltingpoint of antimony, which is 630 C., the arsenic will not condense. butwill remain as a vapor since arsenic sublimes directly into the gaseousstate at a temperature of 615 C. In consequence, the antimony willcondense out as a liquid while the gaseous arsenic passes oif with theother gases through the pipe 33 leading from the condensation chamber 30and may be either condensed to the metal in a second cooler condenser ifthe amount present makes this worth while, or it may be burnt with othergases resulting from the reduction in the recuperator furnace l6 andlater, if desired, separated out as arsenic trioxide.

The solid gangue particles discharged by the conveyor 22 from the hopper2| will contain all the non-volatile impurities in the ore and, if anyprecious metals were originally present in the ore, they will be foundin this gangue and may be easily recovered, along with any other metalsor substances that may be'present in commercially profitable quantities.

In case an oxide ore of antimony is used, the process, as statedheretofore, is essentially the same, save for roasting operation in thevolatilizing chamber IS. The finely pulverized ore would be introducedwith the air for combustion and the reducing medium directly into thefurnace 24 and reduced therein in the manner heretofore described. Thecollection of the anti,- mony droplets and the disposal of the solidgangue particles would be the same as described in connection with thereduction of antimony sulfide.

While air has been specified as the medium for converting the antimonycontent of the ore into fume it is to be understood that equallyfavorable results may be obtained by the use of other mediums, theessential feature in all cases being that the medium employed shallreact chemically with the ore as it passes through the chamber IE tovolatilize the antimony content into fume from which the resultantgangue can be separated as it passes through the collector 20,

while the reduction of antimony sulfide ore to substantially pure metalhas been described, it is to be understood that this was done merely forpurposes of illustration and that the reduction of other ores capable ofbeing roasted to a fume may be accomplished in substantially the samemanner.

Having thus described our invention, we claim:

1. In the method of reducing ore, the steps which include roasting theore to convert a metallic constituent content thereof to fume, and thenreducing the fumed constituent to metal before any substantialcondensation thereof is permitted to take place.

2. In the method of reducing ore, the steps which include powdering theore, roasting the ore to convert a metallic constituent thereof to fume,and then reducing the fumed constituent to metal before any substantialcondensation thereof is permitted to take place.

3. In the method of reducing ore, the steps which include roastin theore to convert a metallic constituent thereof to fume, removing thesolid gangue particles from said fume, and then reducing said fume tometal before any substantial condensation thereof is permitted to takeplace.

4. In the method of reducing antimony ore to metal, the stepswhichinclude so roasting said ore as to convert the antimony content ofthe ore into antimony trioxide fume, and then directing said fume beforeany substantial condensation thereof takes place through a reductionzone to convert said fume into metal.

5. In the method of reducing antimony ore to metal, the steps whichinclude roasting said ore while in gaseous suspension to convert theantimony content of the ore into fume, separating solid gangue particlesfrom the fume,-and then directing the fume before condensation thereofthrough a reducing zone to effect a reduction thereof.

6. In the method of reducing antimony ore to metal, the steps whichinclude directing a stream of oxidizing gas through a roasting chamber,introducing the ore to be treated into said stream, maintaining thetemperature and the composition of the gases in said chamber at valuessufficient to insure the conversion of the antimony content of the oreto fume, during its travel through said chamber, separating solid gangueparticles from the resultant stream of gases and fume, directing theresultant stream of gases and fume before condensation of the fumethrough a, reduction furnace, maintaining in said reduction furnace areducing atmosphere at temperatures sufficient to convert the fumecontent of the stream into metal during its travel through said furnace,and then collecting the antimony metal.

7. The method of reducing antimony ore to metal set forth in claim 6characterized in that waste heat created in the reduction furnace isutilized to maintain the temperature of the stream in the roastingchamber at desired values,

8. The method of reducing antimony ore to metal set forth in claim 6characterized in that the ore is powdered before it is mixed with thestream of oxidizing gas and in that the waste heat from the reductionfurnace is utilized to dry the powdered ore.

9. The method of reducing antimony ore set forth in claim 6characterized in that the waste heat from the reduction furnace isutilized to prevent condensation of the fume during its travel from theroasting chamber to the reduction furnace.

10. The method of reducing antimony ore set forth in claim 6characterized in that the stream of gases and fume is directed upwardlyand then downwardly through the reduction furnace to insure that theconversion of the fume to metal is lecting chamber and in that theresultant stream I of gases and fume from the collecting chamber isdirected upwardly and then downwardly through the reduction furnace toinsure that the conversion ofthe antimony content of the stream to metalis brought about under turbulent conditions.

sure the conversion of the fume to metal in the reduction furnace.

14. The method of reducing antimony ore to metal set forth in claim 6characterized in that a stream of oxidizing gas is intermixed with theresultant gases from the reducing furnace to burn these gases and thusto maintain the temperature of the roasting chamber at desired values.

15. The method of reducing antimony ore to metal set forth in claim 6characterized in that the hot gases and metal from the reduction furnaceare directed through a metal collecting chamber having means forseparating the antimony metal from the gases and maintained at atemperature above the melting point of antimony.

16. In the method of reducing antimony ore, the steps which includeroasting said ore to convert the antimony content thereof into fume, andthen directing the fume thus created before condensation thereof througha violently turbulent reducing zone to effect a rapid reduction thereofto metal.

17. In the method of reducing ore, the steps which include roasting saidoreto convert a metallic constituent thereof to fume, and thensubiecting said fume before condensation thereof to the action ofreducing gas maintained in a turbulent condition to effect a rapidreduction of the fume to metal.

1a. In the method of reducing ore, the steps which include directing astream of the ore to be treated through a roasting chamber, subiectingsaid ore during its travel through said chamber to the action of anoxidizing gas at temperatures sufficient to convert a metallicconstituent thereof to fume, directing the resultant stream of fume andgases before condensation of the fume through a reduction furnace,subjecting said fume during its travel through said reduction furnace tothe action of a reducing agent at temperatures sufficient to effect areduction of the fume to metal, and then separatingvsaid reduced metalfrom the resultant gases.

19. In the method of reducing ore, the steps which include powdering theore to be treated, directing a stream of said powdered ore through aroasting chamber, subjecting said ore during its travel through saidchamber to the action of an oxidizing as at temperatures suiflcient toconvert a metallic constituent thereof into fume, directing theresultant stream of fume and gases before condensation of the fumetogether with a reducing agent and air through a reduction furnace in aviolently turbulent manner to effect a rapid reduction of the fume tometal, and

separating the reduced metal from the resultant stream of gases.

20. In the method of reducing ore, the steps which includes powder-ingthe ore to be treated, directing a stream of said powdered ore through aroasting chamber, subjecting said ore during its travel through saidchamber to the action of an oxidizing gas at temperatures suflicient toconvert a metallic constituent thereof into fume,

directing the resultant stream of fume and gases before condensation ofthe fume together with a reducing agent and air through a reductionfurnace in a violently turbulent manner to effect a rapid reduction ofsaid fume to metal, removing said reduced metal from the resultantgases, and utilizing the resultant gases to preheat the ore prior to itsintroduction into the roasting chamber.

21. In the method of reducing ore, the steps which includes passing astream of oxidizing gas to be treated into said stream, maintaining thetemperature and the composition of the gases in the chamber at. valuessuflicient to effect the conversion of a metallic constituent of the oreinto fume, directing the resultant stream of gases and fume from theroasting chamber together with a reducing agent and air through areduction furnace in a violently turbulent manner to effect a rapidreduction of the fume to metal, and then separating the reduced metalfrom the resultant stream of gases.

22. The method of reducing ore set forth in claim 21 characterized inthat the gases after the reduced metal has been separated therefrom areused to preheat the air stream prior to its introduction into theroasting chamber.

23. In the method of reducing ore, the steps which include passing astream of air through a roasting chamber, introducing the ore to betreated into said stream, maintaining the temperature and compositionof'the gases in the chamber at values sufficient to effect theconversion of a metallic constituent of the ore into fume, directing theresultant stream of gases, fume and solid gangue particles from theroasting chamber through a gangue collecting chamber maintained attemperatures sufliciently high to prevent condensation of the fume,directing the resultant stream of fume and gases from the collectingchamber together with a reducing agent and air through a reductionfurnace in a violently turbulent manner to effect the rapid reduction ofthe fume, and removing the reduce metal from the resultant stream.

24. The method set forth in claim 23 characterized in that the gasesafter the reduced metal has been removed therefrom are'utilized tomain-- tain the temperature of the collecting chamber at desired values.

25. In the method of reducing ore, the steps which include passing astream of air andore to be treated through a roasting chamber,maintaining the temperature and composition of the gases in the chamberat values suflicient to effect the conversion of a metallic constituentof the ore into fume, directing the resultant stream of gases, fume andsolid gangue particles through a collecting chamber to eflect theseparation of the gangue particles from the stream, maintaining thetemperature of said collecting chamber above the condensation point ofthe fume, directing the remaining stream of fume and gases together witha reducing agent and air through a reduction furnace in a violentlyturbulent manner to effect a rapid reduction of the fume, and removingsaid reduced metal from the resultant 26. The method of reducing ore setforth in claim 21 characterized in that the gases after the reducedmetal has been removed therefrom are used to maintain the temperature ofthe roasting chamber at desired values.

27. In the method of reducing ore, the steps which include roasting theore in an atmosphere free of combustion gases to convert a metallicconstituent thereof to fume, and then reducing said fume to metal beforeany substantial condensation thereof is permitted to take place.

FRANK HODSON. CHUNG YU WANG. PETER HODSON.

